Idiopathic bladder stone disease is a major medical problem in Thailand as well as in many other developing countries of the middle East, the Near East and the South-east Asia. The characteristics of the disease are quite similar in the many countries reporting the condition. There is a strong evidence that nutritional component is part of the etiological factors involved in the disease. Data collected in Thailand, Egypt and Pakistan suggest that low levels of available dietary phosphate is the prime nutritional problem which creates an environment conducive to stone formation. The studies suggested in this proposal are expected to provide evidence concerning the efficacy of oral inorganic orthophosphate supplements in preventing bladder stone disease in children and in preventing the presumptive symptoms of the disease and oxalcrystalluria. It is expected that the findings in these studies would be applicable to all countries where this disease is endemic. Ultimately, if phosphate is found to be of prime importance, means must be found to provide phosphate in a more normal manner, since it is recognized that providing supplements to all children may not be feasible in most affected countries.